1. Field of the Invention
The invention is in the field of wavelength measuring devices, particularly those devices utilizing interferometers for measuring the wavelength of monochromatic radiation.
2. Description of the Prior Art
Prior art optical fringe counting techniques are known utilizing interferometers of the Michelson type wherein the optical path length is varied by moving an optical carriage containing a reflecting element within the interferometer system. Interferometers of the Fabry-Perot type have also been widely utilized in studies of coherent radiation as is exemplified, for example, by U.S. Pat. No. 3,824,018 to Crane. In the Crane patent, however, it is necessary to rotate the Fabry-Perot etalon through various angles of incidence inasmuch as no spatial interference pattern is formed. Although wavelength measurements may be made using the resulting frequency pattern as a relative measure, the technique requires movement of the etalon and does not utilize both the spatial frequency (period) and phase of the interferometer pattern to provide an accurate measure of wavelength.